300,000 individuals sustain sports concussions each year in the U.S. The short and long-term effects of sports concussions and sub-concussive impacts are not known, nor are the cumulative effects of repeated injuries understood. What is clear is that there is enormous variability in outcome, although the reasons for this variability are not understood. The overarching theme of this proposal is that an individual's exposure to biomechanical forces is a critical factor influencing outcome. This has two broad components: the characteristics of a single impact (e.g. linear acceleration, rotational acceleration, direction etc.), and the history of exposure to biomechanical forces (e.g. measures of frequency and intensity of impacts over the preceding days and weeks). We propose to use technological advances in on-field head impact monitoring, cognitive testing, and functional brain imaging to learn for the first time what types of head impacts, under what circumstances, in which individuals, cause what effects in brain function. Both acute (post-concussive) and cumulative (pre to one-month post season) monitoring of biomechanical forces are of interest and will be assessed. Three groups of student athletes (football/hockey players with concussion, teammates without concussion, matched non-impact sport athletes) will be studied at three time points (preseason, postseason, and within one week of a concussion) using a standardized cognitive battery and functional MRI (fMRI). Impact parameters will be directly measured using helmet-based accelerometer units. Results of this study should yield important information on the biomechanics and genetics of sports-related traumatic brain injury, lead to more informed return-to-play guidelines, and provide objective information regarding the effects of cumulative minor head injuries.